Wen, H; Malki-Epshtein, L; (2016) A Parametric Study of the Impacts of Pitched Roofs on Flow and Pollution Dispersion in Street Canyons. In: Proceedings of the 3rd IBPSA-England Conference BSO 2016. International Building Performance Simulation Association (IBPSA)-England: Newcastle-upon-Tyne, UK.

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Abstract

This study uses Computational Fluid Dynamics (CFD) to simulate flow and pollutant dispersion in a regular urban structure that consists of six equally spaced street canyons with a centred test street. This structure is known to be adverse for local ventilation and pollutant removal. The impacts of pitch rise and roof arrangement on the flow and dispersion in the test street are studied parametrically. The pitch rise is set in the range of 1–3m, which gives rise-to-run ratios of 2:12–6:12. Four different roof arrangements of flat and pitched roofs on the adjacent buildings of the test street are tested, to give a total of 12 case studies. The case with flat roofs on all the buildings is modelled to provide a reference for comparison. It is found that for all the studied cases, the flow in the test street canyon maintains a single vortex flow pattern. However, all the studied cases have lower velocity and TKE in the test canyon, which leads to reduced ventilation. After analysing the results of each case, we conclude that a high pitch rise and the presence of a pitched roof on the leeward building are the main contributors to this adverse effect. Owing to the lower velocity and TKE, the average pollutant concentration in the canyon is increased in each studied case. In the worst case scenario, the average pollutant concentration is increased by 19%.

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